The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Both active fuel management (AFM) or cylinder deactivation and hybrid propulsion systems may be used to improve fuel economy in vehicles. Cylinder deactivation involves deactivating one or more cylinders of an engine during low load conditions to reduce pumping losses.
Hybrid propulsion systems typically include a first torque generator, such as an internal combustion engine (ICE), and a second torque generator, such as an electric machine (EM). Each can provide torque to a driveline to propel a vehicle. Various configurations of hybrid powertrains can be used, including a strong hybrid powertrain, a mild hybrid powertrain and/or other hybrid types. In a strong hybrid powertrain, the EM can drive the driveline directly, without transferring torque through a component of the ICE.
In a mild hybrid configuration, the EM is coupled with the ICE, such as through the front end accessory drive. Torque generated by the EM is transferred to the driveline through the ICE. An exemplary mild hybrid powertrain includes a belt alternator starter (BAS) system. In the BAS system, the EM is coupled to the ICE via a traditional belt and pulley configuration, which drives other accessory components including, but not limited to, pumps and compressors.
When coupled together, these technologies are capable of providing further fuel savings. One hybrid propulsion efficiency improvement is the engine start-stop feature. During periods where a conventional engine would be idling, the hybrid system stops the engine to increase fuel savings. When the system senses that the driver is about to request the vehicle to accelerate, the hybrid system restarts the engine and may assist the engine in the subsequent vehicle acceleration.
In a system that combines cylinder deactivation with hybrid propulsion, there are times where it is advantageous to deactivate engine cylinders soon after the restart of a hybrid start-stop sequence. Some systems with cylinder deactivation require a time period to completely purge a hydraulic control system of air before cylinder deactivation can occur. For example, a lifter oil manifold assembly (LOMA) and its associated passages in the cylinder block may need to be purged. Current approaches use a predetermined fixed period to allow the purge to occur.
The predetermined fixed period assumes a worst-case condition where the engine off-time completely drains the engine oil galleries of oil. In a non-hybrid vehicle, this delay is not a fuel economy detriment. However in a hybrid vehicle with cylinder deactivation, this delay in deactivating cylinders may be a significant loss in fuel saving opportunity.